1. Field of the Invention
The present invention concerns a battery including a plurality of cylindrical or prismatic cells positioned and connected together, without welding.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Current batteries, in particular those intended for storing the electric energy needed for driving motorized tools, include a large number of elements (sometimes in the hundreds) electrically connected together by contacts formed by conducting lamellae welded to the terminals of said elements which are separated by non-conductors and assembled in the form of packs by an adhesive tape. The manufacture of such batteries requires an assembly which is tedious, time-consuming and costly. Furthermore, they do not allow the replacement of one or several elements which might turn out to be defective, by customer-service or maintenance personnel.
In an application of manufacturing batteries including a small number of elements and intended for supplying the electric energy required for operating small portable equipment such as movie cameras, cameras, compact disc players, a battery without welding has been proposed (U.S. Pat. No. 5,096,788) which includes: a housing with a cover; a plurality of cells positioned in a pair of upper and lower alignment plates and seated in said housing, each cell having a positive and a negative terminal; a flex strip consisting of a single conducting sheet providing the interconnection between the plurality of cells; a first pressure element positioned between the interior surface of the bottom of the housing and a portion of said conducting flex strip; and a second pressure element placed between the cover and another portion of the conducting flex strip, each of said first and second pressure elements being equipped with elastic fingers, said elastic fingers being tilted toward the positive and negative terminals, so as to flatten said opposite portions of the conducting sheet against said terminals and to establish the interconnection of said plurality of cells.
The application of such a device to batteries including a large number of cells does not appear to be feasible. As a matter of fact, in such an application a device of this kind would present at least the following radical drawbacks. The batteries including a large number of cells (for example in the order of a hundred cells) assembled in a parallel connection, generate very strong electrical currents to be flowing through the interconnecting circuits (up to 100 Amperes) which cannot be done with flexstrips. The material used to produce the flexstrips (polyamide or polyester film) is very fragile and can be destroyed by the friction of the contact springs in case of slight movements, which would result in a loss of electrical contact. The springs as described summarily in document U.S. Pat. No. 5,096,788 (springs supposedly cut-outs from sheet metal) do not have sufficient travel and contact force to ensure an efficacious contact of the flex strip on the cell terminals; as a matter of fact, the manufacturing tolerances require a travel of 2 mm and the contact force must be in the order of 2 kg for the contact to be reliable, which cannot be obtained with the device described in the aforementioned document.
The cost of the flex strip is directly dependent on the surface of the latter; one can imagine that it would be very high, if the technology proposed in this document were applied to the manufacture of batteries consisting of a large number of cells to be connected (very large surface to be covered). According to this document, the battery can no longer be disassembled once the cover has been closed by a sealing process.
In an application for the manufacture of batteries including a reduced number of cells, it has been proposed (DE-515 051) to house these cells in a casing closed by a lid. According to this document, a plurality of small flexible tabs is fastened on the underside of the lid, so as to connect each cell with an adjacent cell once said lid is closed. Such a construction implies a very precise and lengthy assembly of the contact tabs which means it can hardly be considered for the manufacture of batteries featuring a large number of cells. Furthermore, the tabs are placed against the cell terminals only under the effect of their own elasticity, yet such pressure is insufficient to guarantee a perennially good contact which may contribute to a reduction in the life of batteries being used in an active manner for professional purposes.
Finally, an application for the manufacture of batteries including a large number of cells, it has been known (EP-1.450.422) to house these cells in a casing that is open on its two sides and to connect them, two by two, by way of small connecting plates that are welded on the opposite ends of said cells.
This connection method has the drawback of requiring elements or cells suitable for welding as well as specialized, costly tooling that is cumbersome and tricky to manipulate in order to execute multiple weldments. Another major drawback of this connection method is that it makes it impossible to disassemble the battery, for example in order to replace one or several defective elements.
Furthermore, the small connecting plates used in the device described by document EP-1 450 422 are not pushed against the poles of the battery elements by individual pressure-providing means but by a collective pressure device including plates of an elastic material such as rubber plates interposed between the terminals of the connected cells and the upper and lower cover plates. Such elastic plates are unable to guarantee continuity of the electrical contact between the small connecting plates and the elements or cells, particularly in case of broken welds.
The invention aims to manufacture batteries including a plurality of elements or cells that are juxtaposed and connected together, without welding or glue, in a simple manner that is faster, more economical, allows disassembly and is highly reliable.